Structure of grids for electron tubes



P" 25, 1967 HIDEO IWAYANAGI STRUCTURE OF GRIDS FOR ELECTRON TUBES Filed Nov. 6, 1963 H1050 I wnvmma ATTORNEY United States Patent 3,316,438 STRUCTURE OF GRIDS FOR ELECTRON TUBES Hideo Iwayanagi, Mobara-shi, Chiba-ken, Japan, assignor to Hitachi, Ltd., Tokyo, Japan, a corporation of Japan Filed Nov. 6, 1963, Ser. No. 321,734 Claims priority, application Japan, Nov. 13, 1962, 37/49,787 3 Claims. (Cl. 313-350) The present invention relates to an improvement in the structure of grid assemblies incorporated in electron tubes.

In the manufacture of a beam tube having a high mutual conductance, spacings between a cathode and grids are made generally smaller in order to obtain a high perveance. In this case, the effect of a periodic field induced by the grid wires is exerted to such a great extent that the threehalves power law is no longer effective at a point of low anode current due to the so-called Inselbildung effect, and any increase in the mutual conductance is thereby limited.

In order to minimize the effect of such periodic electric field, pitches of the grids must be made small. For this, in the beam tube, it is necessary to adjust or align the relative positions of the No. 2 grid wires to the No. 1 grid wires. In a conventional manner of forming the grid assemblies, it has been a matter of difficulty to provide complete alignment of the grid wires as will be described later. Further, the alignment of the grid wires has been extremely difficult as the pitch of the grid wires becomes remarkably small.

The present invention aims at obviating such difficulties, and has for its object to provide a beam tube having an improved grid structure with an extremely high mutual conductance.

According to the invention, there is provided an improved grid block for an electron tube, said grid block being composed of two grid assemblies each comprising a No. 1 grid, a No. 2 grid and ceramic supports therefor, said No. 1 grid being firmly fixed on one face of said ceramic supports, and said No. 2 grid being firmly fixed on the other face of said ceramic supports in such a manner that grid wires of the respective grids are in complete alignment with each other.

There are other objects and particularities of the invention which will be obvious from the following description with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view showing a cathode-grid assembly of a beam tube of conventional prior art structure;

FIG. 2 is a plan view of the cathode-grid assembly of FIG. 1;

FIG. 3 is a perspective view of a cathode-grid block according to the invention comprising an assembly of No. 1 and No. 2 grids and a cathode;

FIG. 4 is a perspective view of the grid assembly of the invention when viewed from the side of an anode;

FIG. 5 is a view similar to FIG. 4 but viewed from the side of a cathode;

FIG. 6 is a plan view of the electrodes as assembled by the use of insulating spacer discs; and

FIG. 7 is an explanatory view showing a manner of cagin g.

In FIGS. 1 and 2, there is shown a conventional prior art structure of a grid assembly wherein No. 1 grid wires 2 and No. 2 grid wires 4 are separately supported by supporting rods 1 and 3, respectively. Centrally of the grid structure, there is disposed a cathode 5. The No. 1 and No. 2 grids are thus formed by the grid wires 2 and 4 wound about the grid supports 1 and 3 which may consist, for example, of metal rods. The grid wires 2 and 4 are ordinarily wound in a manner such that they are spaced apart by a similar pitch or by a different pitch depending upon the expected difference in thermal expansion of the grid supports 1 and 3, respectively, to insure the alignment between the grid wires 2 and 4. However, the grid wires in the known constructions become misaligned during the operation of the electron tube, and the accurate alignment attained during the assembling is entirely lost once the electron tube is placed in operation. Provision of the different pitch is also not effective to insure complete alignment under all operating conditions. Further, the alignment of the No. 1 and No. 2 grids is generally made during the assembling of the grids together with the cathode 5 and other elements, but this operation becomes exceedingly difficult as the pitch of the grid wires is made extremely small.

Such difiiculty is obviated by an improved grid structure according to the invention. FIGS. 3-5 show a grid assembly of an improved structure of the invention. Grid supports 12 are formed by ceramic rods and have a cross section which can provide a desired degree of spacing between No. 1 grid 13 and No. 2 grid 14. The ceramic rods may have a cross section of any suitable shape such as rectangular or any other shape. On opposite sides of each ceramic rod 12, there are provided metalized surfaces 15 and 16 of an elongated and narrow shape which can be produced by sintering a suitable metal such as molybdenum onto each ceramic rod 12. It is needless to say that the metalized surfaces 15 and 16 disposed on the back and front sides, respectively, of the ceramic rods 12 must be electrically insulated from each other.

As shown in FIGS. 4 and 5, the metalized surfaces 15 and 16 on the back and front sides of the ceramic rods 12 are staggered relative to each other so that interelectrode capacitance can be effectively reduced. In straddling relation to the opposing ceramic rods 12, there are provided No. l and No. 2 grid wires 13 and 14, which are firmly fixed on the ceramic rods 12 in the following manner. The grid wires are coated with a suitable metal as by gold plating and are wound about the ceramic rods 12 in a manner that the grid wires are completely aligned with each other on the back and front sides of the grid supports 12. Then the plated metal is molten at a predetermined temperature to thereby obtain soldered connections between the grid wires and the metalized surfaces 15 and 16 on the ceramic rods 12. After soldering, any excess of the grid wires on the sides of the ceramic rods 12 is cut off.

According to such manner of fabrication, it is easy to maintain satisfactory alignment of the grid wires 13 and 14 in the assembly of No. 1 and No. 2 grids. To provide proper reinforcement to the two grid supports 12, a metal strip 17 is fitted to connect the upper ends of the supports 12. For the lower ends of the supports 12, a metal strip 17 is likewise fitted. The metal strips may be soldered to the supports 12 prior to or simultaneously with the soldering of the grid wires on the supports 12, or may be dispensed with when the grid wires 13 and 14 are strong enough for supporting the ceramic supports 12. Or in place of the pair of ceramic rods 12 reinforced with the metal strips 17, a unitary body of a ceramic frame my be used.

FIG. 3 illustrates a cathode-grid block as assembled from two gird assemblies of the invention. The cathodegrid block, shown corresponds to the cathode-grid assembly as shown in FIG. 2. In FIG. 3, there is shown a cathode 11 disposed between the two grid assemblies comprising the No. l and No. 2 grids. The No. 2 grids are connected with each other by a metal ribbon 18 to form a single grid. There are also shown a No. 2 grid con- 3 nector 19,-No. 1 grid connectors 20 and a cathode connector 21.

FIG. 6 shows an arrangement of electrodes wherein the cathode-grid block of FIG. 3 is shown as assembled therein with the use of insulating spacer discs such as of mica. Anodes 22 are supported by anode, supports 23, and cage mica plates 24 have slits 29 and perforations 28 formed therethrough to receive therein the anodes 22 and the anode supports 23, respectively. The cage mica plates 24 have also slits 26 and 27 which are sized to suit the dimensions of the cathode 11 'and the grid supports 12, respectively. The cage mica plates 24 may pref-, erably split into halves as best shown in FIG. 7 so that the grid assemblies as shown in FIGS. 4 and 5 can be snugly fit in the slits 27 in the assembled state by the use of a suitable jig. After all the electrodes have been fitted in the slits of the halves of the cage mica plates 24, these halves are assembled integrally to form the electrode assembly. Then a supporting mica plate 25 is superimposed on the cage mica plate 24, and the anode supports 23 are inserted into the perforations 28 to firmly fix the entire assembly.

Thus, according to the invention, completealignment between the No. 1 grids 13 and the No. 2 grid 14 can be obtained even with an extremely fine pitch of the grid wires, and misalignment due to thermal expansion of the grid supports 12 can be entirely eliminated. Therefore, it is possible to fabricate beam tubes having a high mutual conductance and having an extremely small spacing between the cathode 11 and the grid structure.

What is claimed is:

1. A grid assembly for an electron tube comprising first and second insulating support members positioned in spaced parallel relationship, a first plurality of equally spaced parallel grid wires interconnecting said first and secondsupport members in a first plane tangent to one corresponding side of each support member, and a sec- 0nd plurality of equally spaced parallel grid wires interconnecting said first and second support members in a second plane tangent to a second corresponding side of each support member, said first and second planes being parallel and said first and second grid wires being in complete alignment with each other so that corresponding ones form pairs lying in planes perpendicular to a plane including said support members, first and second metalized surfaces on each of said support rods covering a portion of the area of contact of said grid wires along the entire length of said rods, said grid wires being soldered to the metalized surfaces with which they contact, said rods being of substantially rectangular cross section and said metalized surfaces covering approximately one-half of opposite faces thereof, said metalized surfaces on opposite faces of said rectangular rod being staggered on each rod so as to avoid back to back disposition of said surfaces. v

2. A grid assembly as defined in claim 1 wherein said grid wires are soldered to the metalized surfaces with which they contact.

3. A grid assembly as defined in claim 1 wherein said rods, are supported at their extremities by interconnecting metal strips.

References Cited by the Examiner UNITED STATES PATENTS 2,818,522 12/1957 Wheeler 313-350 2,889,483 6/1959 Kerstetter et al. 313-355 FOREIGN PATENTS 1,064,154 8/1959 Germany.

DAVID J. GALVIN, Primary Examiner.

I. C. HUNGATE, Assistant Examiner. 

1. A GRID ASSEMBLY FOR AN ELECTRON TUBE COMPRISING FIRST AND SECOND INSULATING SUPPORT MEMBERS POSITIONED IN SPACED PARALLEL RELATIONSHIP, A FIRST PLURALITY OF EQUALLY SPACED PARALLEL GRID WIRES INTERCONNECTING SAID FIRST AND SECOND SUPPORT MEMBERS IN A FIRST PLANE TANGENT TO ONE CORRESPONDING SIDE OF EACH SUPPORT MEMBER, AND A SECOND PLURALITY OF EQUALLY SPACED PARALLEL GRID WIRES INTERCONNECTING SAID FIRST AND SECOND SUPPORT MEMBERS IN A SECOND PLANE TANGENT TO A SECOND CORRESPONDING SIDE OF EACH SUPPORT MEMBER, SAID FIRST AND SECOND PLANES BEING PARALLEL AND SAID FIRST AND SECOND GRID WIRES BEING IN COMPLETE ALIGNMENT WITH EACH OTHER SO THAT CORRESPONDING ONES FORM PAIRS LYING IN PLANES PERPENDICULAR TO A PLANE INCLUDING SAID SUPPORT MEMBERS, FIRST AND SECOND METALIZED SURFACES ON EACH OF SAID SUPPORT RODS COVERING A PORTION OF THE AREA OF CONTACT OF SAID GRID WIRES ALONG THE ENTIRE LENGTH OF SAID RODS, SAID GRID WIRES BEING SOLDERED TO THE METALIZED SURFACES WITH WHICH THEY CONTACT, SAID RODS BEING OF SUBSTANTIALLY RECTANGULAR CROSS SECTION AND SAID METALIZED SURFACES COVERING APPROXIMATELY ONE-HALF OF OPPOSITE FACES THEREOF, SAID METALIZED SURFACES ON OPPOSITE FACES OF SAID RECTANGULAR ROD BEING STAGGERED ON EACH ROD SO AS TO AVOID BACK TO BACK DISPOSITION OF SAID SURFACES. 